narrowed
v.v. to become smaller in width or to make something smaller. It can also mean that a list of choices gets shorter as you remove the ones you don't want.
v. to reduce the width or extent of something; to become more restricted or limited. Often used to describe physical spaces or abstract ranges like options and possibilities.
The road narrowed as we drove into the mountains.
The search committee narrowed the list of candidates down to three finalists after the first round of interviews.
As the investigation progressed, the detectives narrowed their focus to a single suspect who had no alibi for the night in question.
Often used with the particle 'down' when referring to a selection process ('narrowed down').
The gap narrowed itselfThe gap narrowedNarrow is often used intransitively to describe a change in state; adding a reflexive pronoun is unnecessary and unnatural.